Typically, display systems generate images from three or more primary colors. Some light sources (e.g. LED, OLED, laser especially) can only produce a narrow range of wavelength. Each primary will be emitted from a separate source (or group of sources). The light from all the sources in the system can be mixed in varying quantities to generate any color within the gamut of the primaries (e.g., by using Grassman's Law of Additivity).
Characteristically, lasers and LEDs/OLEDs have a very narrow spectrum around a center frequency (or inversely, the wavelength), so the colored light that is produced contains only substantially a very exact color.
Human beings all view color slightly differently, i.e. different people are more sensitive to certain hues of reds, greens, and blues. Humans can be thought to have color filters embedded in their eyes which yellow slightly with age. Thus, when two observers look at an identical very specific hue of red (or other color) they may report different intensities relative to other colors observed in the ambient environment.
This effect may be compounded by colors generated by narrow spectrum sources. With a display system comprised of narrow band primaries, two observers may perceive different projected colors due to slight variances in cone wavelength sensitivity. This effect is often referred to as “metameric failure”, and may not be desirable by the designers of display systems comprising narrow spectrum sources.